1861.] KEY BOVEY DEPOSIT. 15 



Such is the manner in "which the clays and other beds filling the 

 basin are arranged ; but, to complete the sketch, a description of the 

 " Head " (seen in the various sections), covering the more regularly 

 stratified beds, is necessary. 



Lying unconformably on the upturned edges of the clay-beds, and 

 becoming considerably deeper towards the centre of the basin (in 

 some places 30 to 40 ft., in others not more than 3 feet deep), is an 

 accumulation of clay, earthy matter, gravel, roUed stones, and boul- 

 ders, with but httle stratification. This is called the " Head "*. In 

 some places the gravel and boulders, in others the earth and clay, 

 preponderate ; and in many places the " Head" partakes of the cha- 

 racter of the adjacent hills, particularly if they be of loose material. 

 At the Decoy, for instance, the " Head" is composed of flint-nodules, 

 quartz, bouldere, and gravel, mixed with clay and earthy matter, 

 and containing also the fossils proper to the adjoining hiUs. In the 

 upper portion of the basin, the " Head " is composed of boulders of 

 schorl, quartz, and slate, with sand and gravel. 



In the low marshes near I^ewton, the " Head " over the clay-beds 

 is stmtified in the following manner : — From the surface to the depth 

 of 3 to 5 feet, loose silt, without shells ; then from 3 inches to 2 feet 

 of dark silt, containing a very few shells of the oyster and cockle, 

 and a great number of the shells now common in the estuary below. 

 Immediately under the silt containing shells, in one place, there is a 

 narrow basin-shaped stratum of peat, from 3 to 18 inches thick, 

 lying on which I found the rib and jaw of a Deer. Below the 

 peat is coarse clay from 6 to 7 feet thick, in which are boulders of 

 granite, slate, and quartz ; and then the true stratified beds of 

 clay. 



The shelly bed described above is not found in the higher portions 

 of the basin, but only near where the Eiver Teign runs into the salt 

 water ; indeed the shells are all found under high -water mark. 



Materials and prohahle mode of formation of the Bovey Deposit. — 

 On submitting the pipe-clay to analysis it is found to contain aboutf 

 63 per cent, of sihca, 27 to 29 per cent, of alumina, some oxide of 

 iron, and a trace of lime. The stifi" clay has considerably more silica, 

 and in larger particles ; the potter's clay nearly the same amount of 

 silica and alumina as the pipe-clay, with a little carbon, from the 

 lignite, I suppose, to which it also owes its dark colour. 



The sand and silty beds on and under the clay are composed 

 chiefly of minute pieces of quartz, with some schorl and slate ; and 

 in the finer beds of silt there are also numerous shining particles of 

 mica. 



The greater part of the materials composing the Bovey deposit 

 are, therefore, identical with the component parts of gi'anite, or such 



♦ Some account of the "Head," and of its local differences, is given by Mr. 

 Godwin-Austen at pp. 438 & 440 of his Memoir, Geol, Trans. 2nd ser. vol. vi. — 

 Edit, 



t I say that the pipe-clay contains about 63 per cent, of silica, because all 

 clays being mechanically, and not chemically, combined, samples of pipe- and 

 potter's clay are found to differ much in their relative proportions of silica and 

 alumina. 



